1. Field of the Invention
The present invention relates generally to the preparation of substrates such as those used in semiconductor fabrication as well as in the manufacture of hard disk drives, and more particularly to a stop for pin lifter devices configured to raise and lower substrates.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform a variety of substrate preparation and fabrication operations in which substrates such as silicon wafers are manipulated within a process environment such as a process chamber. A common method of substrate manipulation is the use of lift pins that are configured to contact a wafer, typically on a back side or non-active surface of the substrate, and with a minimum of surface area contact. In the plurality of fabrication processes that may be performed in a process chamber, the substrate may be raised or lowered as required for both manipulation within the process chamber as well as in preparation for insertion into and removal from the process chamber.
In the prior art, lift pins are configured to raise and lower a substrate between constant, fixed positions in a processing environment such as a process chamber. FIG. 1A shows a typical lift pin assembly 10 within a process chamber. Lift pins 16 are attached to a yoke 20, and travel through a support chuck 14 to a back side of a wafer 12. When a wafer is to be lifted, the lift pins 16 are configured to contact the back side of the wafer 12 in at least three points to raise the wafer 12 off the support chuck 14. The lift pins 16 then withdraw through the support chuck 14 and lower the wafer 12 on to the support chuck 14. As is known, when a wafer 12 is disposed on the support chuck 14, there is no contact between the lift pins 16 and the wafer 12. Bellows 18 are configured around each of the lift pins 16 between the support chuck 14 and the yoke 20 enclosing the lift pins 16 and preventing any contamination of the portion of the lift pin that travels through the support chuck 14.
The yoke 20 is attached to a shaft 22 which is raised and lowered by an actuator 24. The actuator is typically pneumatic, and can also be electrical. The raising and lowering of shaft 22 raises and lowers the yoke 20 which raises and lowers the lift pins 16 in contact with the wafer 12. The actuator 24 receives pneumatic supply, or electrical power and control through cable 26.
The lower portion of the lift pin assembly 10 includes the lift pin stops 30, 32. An upper pin stop 30 is inserted through an upper pin stop housing plate 28. The upper pin stop housing plate is connected to shaft 22. Contact between the upper pin stop 30 and an upper pin stop plate 35 halts upward travel of the shaft 22 and raising of the lift pins 16.
A lower pin stop 32 is inserted through a lower pin stop housing plate 34. Contact between the upper pin stop housing plate 28 and the lower pin stop 32 halts downward travel of the shaft 22 and lowering of the lift pins 16.
FIG. 1B shows a closer view of upper pin stop 30 shown in FIG. 1A. As described in reference to FIG. 1A, the upper pin stop housing plate 28 is attached to shaft 22 (not shown in FIG. 1B). As the lift pin assembly 10 lifts the wafer 12, upper pin stop housing 28 travels upward closing a gap 38 between upper pin stop housing plate 28 and upper pin stop plate 35. Upward travel of upper pin stop housing plate 28 is halted by contact between a tip 36 of upper pin stop 30 and upper pin stop plate 35. Upper pin stop 30 thus stops the raising of lift pins 16 and the wafer 12.
FIG. 1B shows that upper pin stop 30 is configured through upper pin stop housing plate 28. Typically, pin stops 30 and 32 are threaded to provide for adjustment of the pin stop 30, 32 position in housing plates 28, 34. The position of the upper pin stop 30 is therefore adjustable by raising or lowering the upper pin stop 30 in upper pin stop housing plate 28. Adjustment of upper pin stop 30 sets the upper extent of the lift pin assembly 10 by establishing the point at which upper travel of upper pin stop housing plate 28 is halted. In a similar manner, the lower pin stop 32 (See FIG. 1A) sets the lower extent of the lift pin assembly 10.
As can be seen in FIG. 1B, the contact between the tip 36 of upper pin stop 30 and the upper pin stop plate 35 that halts upward travel is a direct, surface to surface contact. In some prior art applications, the material from which the upper pin stop plate 35 is constructed is metal, and the material from which the upper pin stop 30 is constructed is metal, and so the resulting contact is metal to metal contact. In some prior art applications, the upper pin stop 30 has been constructed of a hard plastic, and so the resulting contact is hard plastic to metal. Additionally, some prior art applications incorporate hard plastic layers over the contact areas, also known as stopping surfaces, of upper pin stop housing plate 28 (See FIG. 1A) and upper pin stop plate 35.
Each of the above described types of contact used in a pin stop assembly 10 result in problems with prior art pin stops. In the configuration where a metal pin stop 30, contacts a metal upper pin stop plate 35, the result is an abrupt, hard stop. An abrupt, hard stop is a rapid deceleration caused by hard surface to surface contact typically causing lift pin 16 vibration, bounce, or noise. The metal to metal hard stop can be so abrupt and hard that wafer 12 shifting on the lift pins 16 can result, and in some cases, wafer 12 fracture. Wafer 12 shifting, however slight, can be detrimental to process operations. By way of example, in plasma etching operations, wafer shifting introduces intolerable variance into the process.
The use of hard plastic pin stops or the use of hard plastic layers over the stopping surfaces and resulting hard plastic to metal contact can dampen an abrupt hard stop, but introduces inaccuracies in wafer 12 positioning. Over time, hard plastic exhibits deformation. The deformation results in a change in wafer 12 positioning, and a known requirement in wafer processing is constant, predictable wafer 12 positioning. Hard plastic deformation can result from repeated impact and contact in accordance with pin stop function and design, and can be exacerbated by heat. The deformation of hard plastic used in a hard plastic to metal contact configuration introduces an unacceptable variance.
One approach, as described above, to mitigating the problems associated with hard stops is to re-configure the metal to metal contact by, for example, introducing a hard plastic alternative. It has been found that hard plastic is generally unacceptable, as already described. Another approach to the hard stop problems is to mechanically dampen the movement of the shaft 22 (See FIG. 1A) at the actuator 24 (See FIG. 1A). Unfortunately, known mechanical dampening techniques require more space than is available within a process chamber, and tend to contribute unacceptable cost to design and manufacture.
In view of the foregoing, there is a need to develop and implement a pin stop that can be easily and inexpensively utilized in all manner of substrate lift pin assemblies. The pin stop design should be able to be implemented in existing lift pin assemblies such as those within semiconductor wafer process chambers with a minimum of available space. The pin stop should reduce or eliminate the prior art problems caused by hard stops resulting in wafer shifting or breakage.
Broadly speaking, the present invention fills these needs by providing a simple pin stop that is easily integrated into existing systems and assemblies, and produces a consistent, repeatable, and reliable pin stop while minimizing and eliminating unacceptable wafer shifting or breakage. The present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several embodiments of the present invention are described below.
In one embodiment, a yoke having a plurality of lift pins for the lifting and lowering of a substrate and connected to a pin stop housing plate is provided. The pin stop housing plate includes a pin stop having a head. In the head of the pin stop is a face in which is configured a contact surface that is designed to halt movement of the yoke when the contact surface abuts a stop surface. The contact surface includes a hard stop and a soft stop. The soft stop is configured to compress against the stop surface until the stop surface meets the hard stop.
In another embodiment, an apparatus for stopping movement of a yoke used in a wafer processing system is provided. The apparatus includes a pin shaft and a head connected to the pin shaft. The head has a contact surface that is defined by a hard stop and a soft stop. The hard stop and the soft stop are configured to impact a stopping surface to halt movement of the yoke. The head also has a recess for receiving the soft stop. The soft stop is configured to compress against the stopping surface until the hard stop meets the stopping surface.
In still a further embodiment, a pin stop for stopping movement of a lift pin assembly is provided. The lift pin assembly has a yoke with a set of lift pins and a shaft that moves the yoke into a down position and an up position. The shaft has a yoke connection end connecting the shaft to the yoke, and a stop connection end connecting the shaft to a pin shaft. The pin shaft has a head which has a hard stop and a soft stop. The hard stop and the soft stop are configured to impact a stopping surface and halt the movement of the shaft. The soft stop is configured to compress against the stopping surface until the hard stop contacts the stopping surface.
In yet another embodiment, a method for controlling an abrupt stopping motion of a shaft is provided. The method includes moving a contact surface toward a stopping surface and then absorbing an initial impact between the contact surface and the stopping surface. The absorbing is designed to compress a soft stop component of the contact surface. The method then provides for halting the movement of the contact surface when a hard stop component of the contact surface meets the stopping surface.
The advantages of the present invention are numerous. One notable benefit and advantage of the invention is the elimination of unacceptable wafer shifting or breakage resulting from current hard stop apparatus. By combining the dampening effects of a soft stop with the constant, repeatable and reliable wafer positioning of a hard stop, a lift pin stop is provided that is simple in design and easily implemented to increase reliability of substrate processing and handling.
Another significant advantage is the simplicity of design of the present invention. Although mechanical dampening of the pin stop might produce desirable results, such dampening implementations require space and complexity for various apparatus that are not feasible for process chamber applications. The present invention provides a simple design that is easily implemented in existing and future applications without requiring additional space or complexity. Space considerations are particularly stringent requirements in process chamber applications, and the present invention provides the notable advantage of being easily implemented in process chambers. Additionally, the present invention provides a notable cost savings by being economical to manufacture and install, and by reducing cost of manufacture by reducing or eliminating wafer shifting or breakage and resulting scrap losses.